1. Field of the Invention
This invention relates to a system of forming fiber reinforced organic resins. Particularly it relates to a system for forming twisted pultruded articles reinforced with glass fibers.
2. Prior Art
Reinforcing members formed of fiber reinforced organic resins are quite valuable because of their high strength to weight ratios. Thus, fiber reinforced members having uniform surfaces are typically employed in the reinforcement of concrete, plastics and the like.
A problem associated with the reinforcement of materials such as concrete with fiber reinforced resinous rods is the lack of a mechanical bond between the concrete and exterior surface of the rod. Thus, it is desirable to form a reinforcing member having one or more grooves and/or protrusions on its surface to provide regions for mechanical bonding between the rod surface and the material or matrix to be reinforced.
However, with the known techniques for forming continuous fiber reinforced plastics, the molding of ridges and/or grooves into a reinforcing member severely reduces the strength of the member. In the past, in order to provide ridges or grooves on the surface of a continuous fiber reinforced member, the continuous fibers would be severely bent into the ridges or out of the grooves from their normal longitudinal position along the rod resulting in ridges which have a scarcity of fiber reinforcement therein or reinforcement in an undesired direction. In either case, the reduced amount of continuous fiber reinforcement or the severely bent fibers in the ridges or the reorientation of fibers to form the grooves in the surface substantially reduces the strength of the member at these points. Typical of the prior art reinforcing members having uneven surfaces are those found in U.S. Pat. Nos. 2,510,693; 2,949,054; and 3,859,409.
It is desirable, therefore, to produce a fiber reinforced, resinous rod-like reinforcing bar in which one or more grooves and/or ridges are provided on the surface of the rod along its length to provide mechanical bonding between the reinforcing member and material or matrix to be reinforced and in which the reinforcing fibers in the ridges or surrounding the grooves generally follow the pattern of the ridges and grooves on the surface of the rod to provide higher strength to the reinforcing member than has been previously possible. These grooves and/or ridges are continuous and preferably generally helical in configuration.
Pultrusion is a known method for producing continuous fiber reinforced organic resin articles having uniform shapes along their length. Typical of the known pultrusion processes are those found in U.S. Pat. Nos. 2,721,599; 2,625,498; 3,895,896; and 3,979,493. An inherent problem of the known pultrusion methods is their inability to form shaped articles having other than a regular longitudinal shape. Pultrusion is, however, becaue of its continuous nature, an effective way of producing continuous fiber reinforced stock materials. It would be highly desirable, therefore, to provide a pultrusion method and apparatus capable of producing articles having shapes other than the uniform longitudinal shapes commonly associated with pultrusion.
The U.S. Pat. No. 3,283,050 to Boggs discloses a method and apparatus for making threaded fiber reinforced resin articles. In the system of Boggs the threaded reinforced member is unscrewed from a rotating mold as it is formed. The reinforcement does not follow the flights of the screws.
In the U.S. Pat. No. 3,441,637 to Davis there is disclosed a method for making drink stirrers that comprise a hollow body having a rib on its surface. The hollow plastic tube is twisted as it passes through a heated bath. There are no reinforcing fibers present.
U.S. Pat. No. 2,434,533 to Wurzburger discloses the formation of imitation filaments and ropes and suggests the use of a rotating shaping orifice at column 3, lines 58-75.
There has been disclosed in U.S. patent application, Ser. No. 867,852, filed Jan. 9, 1978, a system for forming twisted reinforced pultruded rods. However, there remains a need for a system that will allow continuous production of uniform twisted rods without the difficulties of over twisting of some portions during forming, inability to run for long periods of time and non-uniform twist.